Critical period of weed interference in irrigated common bean (Phaseolus vulgaris L.) in Dongola area

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1 Critical period of weed interference in irrigated common bean (Phaseolus vulgaris L.) in Dongola area Mukhtar A. Mohamed Faculty of Agricultural Sciences, Dongola University, ElSelaim-Sudan. ABSTRACT: This study was conducted at the Faculty of Agricultural Sciences farm, University of Dongola, El Selaim, during 2010/2011 and 2011/2012 winter seasons to investigate common bean (Phaseolus vulgaris L.) yield loss due to weeds and identify the critical period for weed control. Common bean was sown on 23 November in both seasons. A set of weeding regimes comprising of 12 treatments was arranged in randomized complete block design with four replicates. The crop was kept weed-free for 2, 4, 6, 8 or 10 weeks after sowing and afterward remained weedy till harvest or kept weedy for the same periods and then remained weed- free till harvest. Weed free and weedy treatments, till harvest, were included as controls. Combined analysis of both seasons indicated that unrestricted weed growth significantly reduced common bean grain yield by 57.98% compared to the weed free treatment. Yield decreased as the duration of the weed infestation increased. Plant height was significantly reduced by 45.95% under full season weedy conditions. The same trend was observed for number of leaves/plant, shoot fresh weight/plant and shoot dry weight/plant. The critical period of weed competition was found to be between 4-6 weeks after planting. KEYWORDS: Critical period, weed competition, weeding regimes INTRODUCTION Common bean (Phaseolus vulgaris L.) is an important food legume in Sudan. It is the second important food legume after faba bean in the Northern State. It is planted in the fertile strip of alluvial soils of the Nile valley, on both banks of the Nile river, from Khartoum to Wadi Halfa. The crop is an important source of protein for a major sector of the population, particularly, in urban areas. Furthermore, it is of significant economic importance to farmers (1,2). Weeds constitute one of the main constraints in legumes production in Sudan. They reduce yield and indirectly interfere with the use of land and water resources and adversely affect human welfare (3). Unrestricted weed growth promotes soil degradation in cultivated lands and reduces yield of arable crops by % (4). The magnitude of yield losses due to weeds in common bean in Dongola area has not been estimated. However, yield losses of up to 80% in similar crops such as faba bean, chickpea and lentil were reported (5). The traditional method for controlling weeds in legumes in Northern Sudan is late hand-weeding which is carried out, voluntarily, by farmers to collect fodder for livestock. Hand weeding is labour intensive, tedious, laborious, time consuming, and is therefore expensive when done by hired labour. The yield losses are mainly due to delayed weeding or insufficient weed control (5, 6). The critical period for weed interference is defined as the period in the crop growth cycle during which weeds must be controlled to prevent unacceptable yield losses (7). Weeds removal during this period is mandatory to optimize weed control. It enables decision making on the need for and timing of efficient weed Control (8). Generally, the critical period for weed interference is influenced by many factors such as weed species, the environment, and 1

2 plant density, time of competition, soil fertility and crop cultivar (7, 8). The critical delay in weeding for most crops was found to be 4-6 weeks and when weeding starts at 6 weeks after sowing, yield losses amount to % (9). Information on the competitive ability of weeds in common bean is lacking in Sudan. This study was, therefore, conducted to investigate yield loss due to weeds and identify the critical period for weed interference. MATERIALS and METHODS An experiment was conducted at the Faculty of Agricultural Sciences farm, University of Dongola, El Selaim, Northern State, Sudan. The State is located within latitude 16 and 22 N, and longitude 20 and 32 E. The area is a true desert with extremely high temperatures and radiation in summer, low temperature in winter, scarce rainfall and high wind speed. The mean maximum and minimum temperatures are 36.8 and 19.5 C, respectively. The climate is hyper arid with a vapour pressure of only 10.8 mb and a relative humidity less than 20% (10). The experimental site was disc ploughed, harrowed, leveled, and divided into plots in each season. Plot size was 3 2 m. Each plot consisted of six rows, each two meters long. Common bean, variety Balady, was sown on 23 November during 2010/2011 and 2011/2012 seasons at Dongola, Northern State, Sudan. Three seeds/hole were planted in rows 60 cm apart and 20 cm between holes, on flat plots. Seedlings were thinned to two plants/hole two weeks after planting resulting in approximately plants/feddan. Weeding regimes, comprising of 12 treatments, were arranged in randomized complete block design with four replicates. The crop was kept weed-free for 2, 4, 6, 8 or 10 weeks after crop sowing and later remained weedy till harvest or kept weedy for the same periods and then maintained weed- free till harvest in both seasons. Weed-free and weedy treatments till harvest were included as controls. In the weed- free treatment, weeds were removed by repeated hand weeding to keep the crop free from weeds up to harvest. However, in the weedy treatment, weeds were left to grow, unrestrictedly, with the crop until harvest. Nitrogen fertilizer, in the form of urea, was applied at 43 kg /ha immediately after thinning before the third irrigation. Irrigation was applied at days interval depending on temperature and other environmental conditions. Cultural practices were carried as recommended by the Agricultural Research Corporation recommendations (5, 10). At eight weeks after sowing ten plants were randomly selected from the four inner rows in each plot. Plant height, number of leaves/plant, shoots fresh weight/plant and shoot dry weight/plant was measured. At harvest, pods from ten randomly selected plants were collected and mean number of pods/plant, mean number of seeds/pod were recorded. Pods were air dried, threshed and 100 seed weight determined. The harvested area (m 2 ) from each plot was air dried and threshed in bulk, then weighted and the total grain yield (kg/ha) was calculated. The data was subjected to analysis of variance and means were separated using the Duncan s Multiple Range Test. 2

3 RESULTS and DISCUSSION The weed flora in the experimental site consisted of grassy and broad-leaved weeds. The dominant weed species were Cynodon dactylon (L.) pers., Sorghum arundinaceum. (Dew.) Stapl, Tribulus terrestris L., Amaranthus viridis L., Sonchus oleraceus L., Eruca sativa Mill., Amaranthus graecizans L., Euphorbia aegyptiaca Boiss., Solanum nigrum L. and Trigonella hamosa L. Combined analysis of both seasons indicated that unrestricted weed growth accounted for 57.98% loss in common bean yield, compared with the weed-free out (Table 1). Similar results were reported by several workers (5,11,12) that, reductions in yield of common beans due to weeds ranged from 24-74%. Findings reported by Mohamed et al., (13) and Khogali et al., (5) indicated that yield losses due to weeds in similar crops such as faba bean, chickpea and lentil are more than 50%. Losses due to weeds ware a result of competition for water, nutrients and light and because of the low competitive ability of the legume crops during the early stages of growth. Early removal of weeds will, therefore, enable the crop to maximize the use of the available resources. Common bean grain yield decreased as the duration of weed infestation increased. This finding is in line with that of reported by Worwick and Black (16) who showed that, crop grain yield reduction by weeds was directly related to the duration of weed interference. The reduction in common bean grain yield due to weeds interference was mainly through reduction in number of seeds/pod and 100 seed weight (Table 1 and 2). The critical period of weed interference in common bean was between 4 and 6 weeks after crop planting (Table 1). The critical period for weed competition in most crops was reported to be between 4 and 6 weeks after sowing (9). Dawood (14) (15) and Mukhtar showed that, the fourth week after sowing is the most critical period of weed control in faba bean. This difference in the critical period is expected, because the critical period for weed control is influenced by several factors including weed species, density or ground cover by weeds, the environment, plant density, time of weed competition, soil fertility and crop cultivar (4, 7). Common bean Growth parameters were also adversely affected by weed competition. Plant height was significantly reduced by 45.95% under full season weed competition. The same trend was also observed for number of leaves/plant, shoot fresh weight/plant and shoot dry weight/plant (Table 2). It is evident that a weed-free period starting from the 4 th to the 6 th week after sowing is necessary to provide high grain yield. To attain weed-free environment in common bean, pre or post-emergence herbicides, mechanical and haweeding should be timed and adjusted to the critical period of weed competition only. In this, way use of persistent soil acting herbicides could be avoided and weed control treatments minimized. CONCLUSIONS Combined analysis of the data for the two seasons indicated that unrestricted weed growth was accounted for 57.98% loss in common bean yield. Grain yield decreased as the duration of weed infestation increased. The reduction in yield due to weeds 3

4 interference was mainly through reduction in number of seeds/pod and 100 seed weight. The critical period of weed competition was between 4 and 6 weeks after crop planting Table 1: Combined influence of duration of weed interference on grain yield and yield components during both winter seasons, Treatments No. of pods/plant No. of seeds/pod 100 seed weight (g) Grain yield (kg/ha) Weed-free for 2 weeks 8.40a 3.28cd 20.00bc e Weed-free for 4 weeks 9.30a 4.00bc 20.40bc d Weed-free for 6 weeks 9.70a 4.62ab 21.15bc d Weed-free for 8 weeks 9.50a 5.10a 21.10b c Weed-free for 10 weeks 9.10a 5.20a 20.90bc b Weedy for 2 weeks 7.90a 4.50ab 20.10bc f Weedy for 4 weeks 7.50a 3.50bcd 19.80bc g Weedy for 6 weeks 7.20a 3.30cd 19.10bc 593.1h Weedy for 8 weeks 7.10a 3.20cd 20.10bc h Weedy for 10 weeks 6.40a 2.90d 17.90c h Full season weed-free control 9.20a 5.20a 29.50a a Full season weedy control 6.60a 3.20cd 18.40bc h C. V% S. E.± Means with the same letters in the same column are not significantly different at p 0.05 level of probability according to DMRT. 4

5 Table 2: Combined influence of duration of weed interference on common bean growth parameters during both winter season. Treatments Plant height (cm) No. of leaves/plant Shoot fresh wt (g)/plant Shoot dry wt (g)/plant Weed-free for 2 weeks 50.30c 62.00bc 31cd 7.30bc Weed-free for 4 weeks 61.20b 66.10abc 34.20bc 6.80c Weed-free for 6 weeks 61.10b 68.50ab 42ab 8.10abc Weed-free for 8 weeks 65.70b 69.40ab 47.10a 8.70abc Weed-free for 10 weeks 79.20a 71.90ab 49.90a 9.90ab Weedy for 2 weeks 39.90e 57.80cd 24.00d 6.40c Weedy for 4 weeks 45.00cde 54.00de 22.80d 6.40c Weedy for 6 weeks 47.10cde 48.40de 20.00d 6.30c Weedy for 8 weeks 40.00e 48.20de 22.40d 6.60c Weedy for 10 weeks 48.90cd 47.40de 21.20d 7.00c Full season weed-free control 80.30a 76.10a 45.70a 10.00a Full season weedy control 43.40de 43.90e 21.70d 6.30c C. V% S. E.± Means with the same letters in the same column are not significantly different at 0.05 level of probability according to DMRT. REFERENCES 1. Babiker, A. G. T., Ahmed, E. A.,Dawoud, D. A. and Abdella, N. K. (2007). Orobanche species in Sudan: History, distribution and management. Sudan Journal of Agricultural Research 10: Elballa, M. M. A., El-amin, A. H.B.,Elamin, E.A. and Elsheikh, E. A. E. (2004). Interactive effects of cultivars, foliar application of micronutrients and Rhizobium inoculation on snap bean (Phaseolus vulgaris L.) performance. University of Khartoum Journal of Agricultural Sciences 12: Hamada, A. A.; Eltahir, S. A. and Mukhtar, A. M. (2009). Weed survey on maize (Zea mays L.) in Dongola area, Northern State, Sudan. Sudan Journal of Agricultural Research 13,

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